1. Field of the Invention
The present invention relates to an applicator and method for the delivery of Vitamin C (ascorbic acid), especially for the topical delivery to a patient's skin. More particularly, the present invention relates to a multiple-compartment transdermal drug delivery device and delivery method for ascorbic acid in which a first compartment and a second compartment are concentrically located. One compartment houses a dry powder form of ascorbic acid, and the second compartment houses a solution or other suitable carrier. Just prior to use, the contents of the two compartments are mixed together, thus maintaining maximum efficacy of the ascorbic acid when applied to the skin surface.
2. Description of Related Art
The present invention relates to a device for the topical or transdermal delivery of Vitamin C (ascorbic acid) and its pharmaceutically acceptable salts and esters. Ascorbic acid has many known biological functions from enzymatic co-factor to “sparing” agent against Vitamin E depletion. The latter function may partly account for its “antioxidant” status. Additionally, at higher concentrations, ascorbic acid is known to react with both superoxide and hydroxyl radicals. Superoxide and the subsequently generated hydrogen peroxide and hydroxyl radical are oxygen-containing free radicals now known to be generated in vivo under a variety of normal and pathological conditions. Quite simply, these radicals have been implicated as causative agents for everything from sunburn to aging. These radicals destroy lipid membranes, breakdown DNA, inactivate enzymes, and so forth.
Ascorbic acid is also thought to be involved in wound healing. The process of wound healing generally encompasses three phases during which the injured tissue is repaired, regenerated, and new tissue is reorganized into a scar. These three phases are classified as: (a) an inflammation phase which begins from about day 0 to 3 days, (b) a cellular proliferation phase from about 3 to 12 days, and (c) a remodeling phase from about 3 days to about 6 months. In all three phases, antioxidants, such as Vitamin C, play a vital role in the healing process.
In the inflammation phase, inflammatory cells, mostly neutrophils, enter the site of the wound followed by lymphocytes, monocytes, and later macrophages. The neutrophils that are stimulated begin to release proteases and reactive oxygen species into the surrounding medium with potential adverse effects on both the adjacent tissues and the invading microorganisms.
The proliferative phase consists of laying down new granulation tissue, and the formation of new blood vessels in the injured area. The fibroblasts, endothelial cells, and epithelial cells migrate in the wound site. These fibroblasts produce the collagen that is necessary for wound repair. Ascorbic acid is crucial in the formation of collagen. Several studies have demonstrated that ascorbic acid was capable of overcoming the reduced proliferative capacity of elderly dermal fibroblasts, as well as increasing collagen synthesis in elderly cells by similar degrees as in newborn cells even though the basal levels of collagen synthesis are age dependent. A decrease of ascorbic acid at the injury area will decrease the rate of wound healing.
In reepithelialization, epithelial cells migrate from the free edges of the tissue across the wound. This event is succeeded by the proliferation of epithelial cells at the periphery of the wound. Research has also shown that reepithelialization is enhanced by the presence of occlusive wound dressings which maintain a moisture barrier.
The final phase of wound healing, which is remodeling, is effected by both the replacement of granulation tissue with collagen and elastin fibers and the devascularization of the granulation tissue. Recent studies have shown that topical application of antioxidants reduces scarring and normalizes blood coagulation during therapy.
L-Ascorbic acid is chemically defined as an alpha-keto-lactone and containing an acid-ionizable hydrogen in water (pK=4.2). Ascorbic acid is also a moderately strong reductant. These properties, which lead to instability in the ascorbic acid structure, are well known and have been burdensome to pharmacologists when attempting to formulate active ascorbic acid solutions. Thus, at higher pHs values, the ascorbic acid increasingly becomes the notoriously unstable ascorbate anion. This instability may be due to several causes not restricted to stereochemical strain, oxidative degradation, and degradation due to water attack.
For these reasons, among others, scientists working in the field have had difficulty in formulating stable solutions of ascorbic acid which would be useful for cosmetic or dermatological needs. Nevertheless, because of the many beneficial pharmaceutical effects attributed to ascorbic acid, numerous attempts have been made to overcome these difficulties.